The Grianan of Aileach: An Irish Fort Featured on Ptolemy's Map of the World
The Grianan of Aileach (Sun Temple of Aileach) is one of the largest and most impressive circular stone hill top enclosures in the whole of Ireland. The stone fort, which is located in Donegal, Ireland, sits on the top of Greenan Hill, and offers a spectacular view of the surrounding area.
Source: ancient-origins.net